/* ---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
// Some code copied and modified from https://github.com/microsoft/vscode/blob/1.44.0/src/vs/base/common/filters.ts

import { CharCode } from './charCode';
import { LRUCache } from './map';
import { convertSimple2RegExpPattern, startsWithIgnoreCase } from './strings';

// Returns null if word doesn't match.
export type IFilter = (word: string, wordToMatchAgainst: string) => IMatch[] | null;

export interface IMatch {
  start: number;
  end: number;
}

// Combined filters

/**
 * @returns A filter which combines the provided set
 * of filters with an or. The *first* filters that
 * matches defined the return value of the returned
 * filter.
 */
export function or(...filter: IFilter[]): IFilter {
  return function(word: string, wordToMatchAgainst: string): IMatch[] | null {
    for (let i = 0, len = filter.length; i < len; i++) {
      const match = filter[i](word, wordToMatchAgainst);
      if (match) {
        return match;
      }
    }
    return null;
  };
}

// Prefix

export const matchesStrictPrefix: IFilter = _matchesPrefix.bind(undefined, false);
export const matchesPrefix: IFilter = _matchesPrefix.bind(undefined, true);

function _matchesPrefix(ignoreCase: boolean, word: string, wordToMatchAgainst: string): IMatch[] | null {
  if (!wordToMatchAgainst || wordToMatchAgainst.length < word.length) {
    return null;
  }

  let matches: boolean;
  if (ignoreCase) {
    matches = startsWithIgnoreCase(wordToMatchAgainst, word);
  } else {
    matches = wordToMatchAgainst.indexOf(word) === 0;
  }

  if (!matches) {
    return null;
  }

  return word.length > 0 ? [{ start: 0, end: word.length }] : [];
}

// Contiguous Substring

export function matchesContiguousSubString(word: string, wordToMatchAgainst: string): IMatch[] | null {
  const index = wordToMatchAgainst.toLowerCase().indexOf(word.toLowerCase());
  if (index === -1) {
    return null;
  }

  return [{ start: index, end: index + word.length }];
}

// Substring

export function matchesSubString(word: string, wordToMatchAgainst: string): IMatch[] | null {
  return _matchesSubString(word.toLowerCase(), wordToMatchAgainst.toLowerCase(), 0, 0);
}

function _matchesSubString(word: string, wordToMatchAgainst: string, i: number, j: number): IMatch[] | null {
  if (i === word.length) {
    return [];
  } else if (j === wordToMatchAgainst.length) {
    return null;
  } else {
    if (word[i] === wordToMatchAgainst[j]) {
      let result: IMatch[] | null = null;
      if ((result = _matchesSubString(word, wordToMatchAgainst, i + 1, j + 1))) {
        return join({ start: j, end: j + 1 }, result);
      }
      return null;
    }

    return _matchesSubString(word, wordToMatchAgainst, i, j + 1);
  }
}

// CamelCase

function isLower(code: number): boolean {
  return CharCode.a <= code && code <= CharCode.z;
}

export function isUpper(code: number): boolean {
  return CharCode.A <= code && code <= CharCode.Z;
}

function isNumber(code: number): boolean {
  return CharCode.Digit0 <= code && code <= CharCode.Digit9;
}

function isWhitespace(code: number): boolean {
  return (
    code === CharCode.Space || code === CharCode.Tab || code === CharCode.LineFeed || code === CharCode.CarriageReturn
  );
}

const wordSeparators = new Set<number>();
'`~!@#$%^&*()-=+[{]}\\|;:\'",.<>/?'.split('').forEach((s) => wordSeparators.add(s.charCodeAt(0)));

function isWordSeparator(code: number): boolean {
  return isWhitespace(code) || wordSeparators.has(code);
}

function charactersMatch(codeA: number, codeB: number): boolean {
  return codeA === codeB || (isWordSeparator(codeA) && isWordSeparator(codeB));
}

function isAlphanumeric(code: number): boolean {
  return isLower(code) || isUpper(code) || isNumber(code);
}

function join(head: IMatch, tail: IMatch[]): IMatch[] {
  if (tail.length === 0) {
    tail = [head];
  } else if (head.end === tail[0].start) {
    tail[0].start = head.start;
  } else {
    tail.unshift(head);
  }
  return tail;
}

function nextAnchor(camelCaseWord: string, start: number): number {
  for (let i = start; i < camelCaseWord.length; i++) {
    const c = camelCaseWord.charCodeAt(i);
    if (isUpper(c) || isNumber(c) || (i > 0 && !isAlphanumeric(camelCaseWord.charCodeAt(i - 1)))) {
      return i;
    }
  }
  return camelCaseWord.length;
}

function _matchesCamelCase(word: string, camelCaseWord: string, i: number, j: number): IMatch[] | null {
  if (i === word.length) {
    return [];
  } else if (j === camelCaseWord.length) {
    return null;
  } else if (word[i] !== camelCaseWord[j].toLowerCase()) {
    return null;
  } else {
    let result: IMatch[] | null = null;
    let nextUpperIndex = j + 1;
    result = _matchesCamelCase(word, camelCaseWord, i + 1, j + 1);
    while (!result && (nextUpperIndex = nextAnchor(camelCaseWord, nextUpperIndex)) < camelCaseWord.length) {
      result = _matchesCamelCase(word, camelCaseWord, i + 1, nextUpperIndex);
      nextUpperIndex++;
    }
    return result === null ? null : join({ start: j, end: j + 1 }, result);
  }
}

interface ICamelCaseAnalysis {
  upperPercent: number;
  lowerPercent: number;
  alphaPercent: number;
  numericPercent: number;
}

// Heuristic to avoid computing camel case matcher for words that don't
// look like camelCaseWords.
function analyzeCamelCaseWord(word: string): ICamelCaseAnalysis {
  let upper = 0;
  let lower = 0;
  let alpha = 0;
  let numeric = 0;
  let code = 0;

  for (let i = 0; i < word.length; i++) {
    code = word.charCodeAt(i);

    if (isUpper(code)) {
      upper++;
    }
    if (isLower(code)) {
      lower++;
    }
    if (isAlphanumeric(code)) {
      alpha++;
    }
    if (isNumber(code)) {
      numeric++;
    }
  }

  const upperPercent = upper / word.length;
  const lowerPercent = lower / word.length;
  const alphaPercent = alpha / word.length;
  const numericPercent = numeric / word.length;

  return { upperPercent, lowerPercent, alphaPercent, numericPercent };
}

function isUpperCaseWord(analysis: ICamelCaseAnalysis): boolean {
  const { upperPercent, lowerPercent } = analysis;
  return lowerPercent === 0 && upperPercent > 0.6;
}

function isCamelCaseWord(analysis: ICamelCaseAnalysis): boolean {
  const { upperPercent, lowerPercent, alphaPercent, numericPercent } = analysis;
  return lowerPercent > 0.2 && upperPercent < 0.8 && alphaPercent > 0.6 && numericPercent < 0.2;
}

// Heuristic to avoid computing camel case matcher for words that don't
// look like camel case patterns.
function isCamelCasePattern(word: string): boolean {
  let upper = 0;
  let lower = 0;
  let code = 0;
  let whitespace = 0;

  for (let i = 0; i < word.length; i++) {
    code = word.charCodeAt(i);

    if (isUpper(code)) {
      upper++;
    }
    if (isLower(code)) {
      lower++;
    }
    if (isWhitespace(code)) {
      whitespace++;
    }
  }

  if ((upper === 0 || lower === 0) && whitespace === 0) {
    return word.length <= 30;
  } else {
    return upper <= 5;
  }
}

export function matchesCamelCase(word: string, camelCaseWord: string): IMatch[] | null {
  if (!camelCaseWord) {
    return null;
  }

  camelCaseWord = camelCaseWord.trim();

  if (camelCaseWord.length === 0) {
    return null;
  }

  if (!isCamelCasePattern(word)) {
    return null;
  }

  if (camelCaseWord.length > 60) {
    return null;
  }

  const analysis = analyzeCamelCaseWord(camelCaseWord);

  if (!isCamelCaseWord(analysis)) {
    if (!isUpperCaseWord(analysis)) {
      return null;
    }

    camelCaseWord = camelCaseWord.toLowerCase();
  }

  let result: IMatch[] | null = null;
  let i = 0;

  word = word.toLowerCase();
  while (i < camelCaseWord.length && (result = _matchesCamelCase(word, camelCaseWord, 0, i)) === null) {
    i = nextAnchor(camelCaseWord, i + 1);
  }

  return result;
}

// Matches beginning of words supporting non-ASCII languages
// If `contiguous` is true then matches word with beginnings of the words in the target. E.g. "pul" will match "Git: Pull"
// Otherwise also matches sub string of the word with beginnings of the words in the target. E.g. "gp" or "g p" will match "Git: Pull"
// Useful in cases where the target is words (e.g. command labels)

export function matchesWords(word: string, target: string, contiguous = false): IMatch[] | null {
  if (!target || target.length === 0) {
    return null;
  }

  let result: IMatch[] | null = null;
  let i = 0;

  word = word.toLowerCase();
  target = target.toLowerCase();
  while (i < target.length && (result = _matchesWords(word, target, 0, i, contiguous)) === null) {
    i = nextWord(target, i + 1);
  }

  return result;
}

function _matchesWords(word: string, target: string, i: number, j: number, contiguous: boolean): IMatch[] | null {
  if (i === word.length) {
    return [];
  } else if (j === target.length) {
    return null;
  } else if (!charactersMatch(word.charCodeAt(i), target.charCodeAt(j))) {
    return null;
  } else {
    let result: IMatch[] | null = null;
    let nextWordIndex = j + 1;
    result = _matchesWords(word, target, i + 1, j + 1, contiguous);
    if (!contiguous) {
      while (!result && (nextWordIndex = nextWord(target, nextWordIndex)) < target.length) {
        result = _matchesWords(word, target, i + 1, nextWordIndex, contiguous);
        nextWordIndex++;
      }
    }
    return result === null ? null : join({ start: j, end: j + 1 }, result);
  }
}

function nextWord(word: string, start: number): number {
  for (let i = start; i < word.length; i++) {
    if (isWordSeparator(word.charCodeAt(i)) || (i > 0 && isWordSeparator(word.charCodeAt(i - 1)))) {
      return i;
    }
  }
  return word.length;
}

// Fuzzy

const fuzzyContiguousFilter = or(matchesPrefix, matchesCamelCase, matchesContiguousSubString);
const fuzzySeparateFilter = or(matchesPrefix, matchesCamelCase, matchesSubString);
const fuzzyRegExpCache = new LRUCache<string, RegExp>(10000); // bounded to 10000 elements

export function matchesFuzzy(
  word: string,
  wordToMatchAgainst: string,
  enableSeparateSubstringMatching = false
): IMatch[] | null {
  if (typeof word !== 'string' || typeof wordToMatchAgainst !== 'string') {
    return null; // return early for invalid input
  }

  // Form RegExp for wildcard matches
  let regexp = fuzzyRegExpCache.get(word);
  if (!regexp) {
    regexp = new RegExp(convertSimple2RegExpPattern(word), 'i');
    fuzzyRegExpCache.set(word, regexp);
  }

  // RegExp Filter
  const match = regexp.exec(wordToMatchAgainst);
  if (match) {
    return [{ start: match.index, end: match.index + match[0].length }];
  }

  // Default Filter
  return enableSeparateSubstringMatching
    ? fuzzySeparateFilter(word, wordToMatchAgainst)
    : fuzzyContiguousFilter(word, wordToMatchAgainst);
}

/**
 * Match pattern againt word in a fuzzy way. As in IntelliSense and faster and more
 * powerfull than `matchesFuzzy`
 */
export function matchesFuzzy2(pattern: string, word: string): IMatch[] | null {
  const score = fuzzyScore(pattern, pattern.toLowerCase(), 0, word, word.toLowerCase(), 0, true);
  return score ? createMatches(score) : null;
}

export function anyScore(
  pattern: string,
  lowPattern: string,
  _patternPos: number,
  word: string,
  lowWord: string,
  _wordPos: number
): FuzzyScore {
  const result = fuzzyScore(pattern, lowPattern, 0, word, lowWord, 0, true);
  if (result) {
    return result;
  }
  let matches = 0;
  let score = 0;
  let idx = _wordPos;
  for (let patternPos = 0; patternPos < lowPattern.length && patternPos < _maxLen; ++patternPos) {
    const wordPos = lowWord.indexOf(lowPattern.charAt(patternPos), idx);
    if (wordPos >= 0) {
      score += 1;
      matches += 2 ** wordPos;
      idx = wordPos + 1;
    } else if (matches !== 0) {
      // once we have started matching things
      // we need to match the remaining pattern
      // characters
      break;
    }
  }
  return [score, matches, _wordPos];
}

// #region --- fuzzyScore ---

export function createMatches(score: undefined | FuzzyScore): IMatch[] {
  if (typeof score === 'undefined') {
    return [];
  }

  const matches = score[1].toString(2);
  const wordStart = score[2];
  const res: IMatch[] = [];

  for (let pos = wordStart; pos < _maxLen; pos++) {
    if (matches[matches.length - (pos + 1)] === '1') {
      const last = res[res.length - 1];
      if (last && last.end === pos) {
        last.end = pos + 1;
      } else {
        res.push({ start: pos, end: pos + 1 });
      }
    }
  }
  return res;
}

const _maxLen = 128;

function initTable() {
  const table: number[][] = [];
  const row: number[] = [0];
  for (let i = 1; i <= _maxLen; i++) {
    row.push(-i);
  }
  for (let i = 0; i <= _maxLen; i++) {
    const thisRow = row.slice(0);
    thisRow[0] = -i;
    table.push(thisRow);
  }
  return table;
}

const _table = initTable();
const _scores = initTable();
const _arrows = initTable() as Arrow[][];
const _debug = false;

function printTable(table: number[][], pattern: string, patternLen: number, word: string, wordLen: number): string {
  function pad(s: string, n: number, pad = ' ') {
    while (s.length < n) {
      s = pad + s;
    }
    return s;
  }

  let ret = ` |   |${word
    .split('')
    .map((c) => pad(c, 3))
    .join('|')}\n`;

  for (let i = 0; i <= patternLen; i++) {
    if (i === 0) {
      ret += ' |';
    } else {
      ret += `${pattern[i - 1]}|`;
    }
    ret +=
      table[i]
        .slice(0, wordLen + 1)
        .map((n) => pad(n.toString(), 3))
        .join('|') + '\n';
  }
  return ret;
}

function isSeparatorAtPos(value: string, index: number): boolean {
  if (index < 0 || index >= value.length) {
    return false;
  }
  const code = value.charCodeAt(index);
  switch (code) {
    case CharCode.Underline:
    case CharCode.Dash:
    case CharCode.Period:
    case CharCode.Space:
    case CharCode.Slash:
    case CharCode.Backslash:
    case CharCode.SingleQuote:
    case CharCode.DoubleQuote:
    case CharCode.Colon:
    case CharCode.DollarSign:
      return true;
    default:
      return false;
  }
}

function isWhitespaceAtPos(value: string, index: number): boolean {
  if (index < 0 || index >= value.length) {
    return false;
  }
  const code = value.charCodeAt(index);
  switch (code) {
    case CharCode.Space:
    case CharCode.Tab:
      return true;
    default:
      return false;
  }
}

function isUpperCaseAtPos(pos: number, word: string, wordLow: string): boolean {
  return word[pos] !== wordLow[pos];
}

export function isPatternInWord(
  patternLow: string,
  patternPos: number,
  patternLen: number,
  wordLow: string,
  wordPos: number,
  wordLen: number
): boolean {
  while (patternPos < patternLen && wordPos < wordLen) {
    if (patternLow[patternPos] === wordLow[wordPos]) {
      patternPos += 1;
    }
    wordPos += 1;
  }
  return patternPos === patternLen; // pattern must be exhausted
}

const enum Arrow {
  Top = 0b1,
  Diag = 0b10,
  Left = 0b100,
}

/**
 * A tuple of three values.
 * 0. the score
 * 1. the matches encoded as bitmask (2^53)
 * 2. the offset at which matching started
 */
export type FuzzyScore = [number, number, number];

export namespace FuzzyScore {
  /**
   * No matches and value `-100`
   */
  export const Default = Object.freeze([-100, 0, 0]) as [-100, 0, 0];

  export function isDefault(score?: FuzzyScore): score is [-100, 0, 0] {
    return !score || (score[0] === -100 && score[1] === 0 && score[2] === 0);
  }
}

export type FuzzyScorer = (
  pattern: string,
  lowPattern: string,
  patternPos: number,
  word: string,
  lowWord: string,
  wordPos: number,
  firstMatchCanBeWeak: boolean
) => FuzzyScore | undefined;

export function fuzzyScore(
  pattern: string,
  patternLow: string,
  patternPos: number,
  word: string,
  wordLow: string,
  wordPos: number,
  firstMatchCanBeWeak: boolean
): FuzzyScore | undefined {
  const patternLen = pattern.length > _maxLen ? _maxLen : pattern.length;
  const wordLen = word.length > _maxLen ? _maxLen : word.length;

  if (patternPos >= patternLen || wordPos >= wordLen || patternLen > wordLen) {
    return undefined;
  }

  // Run a simple check if the characters of pattern occur
  // (in order) at all in word. If that isn't the case we
  // stop because no match will be possible
  if (!isPatternInWord(patternLow, patternPos, patternLen, wordLow, wordPos, wordLen)) {
    return undefined;
  }

  const patternStartPos = patternPos;
  const wordStartPos = wordPos;

  // There will be a mach, fill in tables
  for (patternPos = patternStartPos + 1; patternPos <= patternLen; patternPos++) {
    for (wordPos = 1; wordPos <= wordLen; wordPos++) {
      let score = -1;
      if (patternLow[patternPos - 1] === wordLow[wordPos - 1]) {
        if (wordPos === patternPos - patternStartPos) {
          // common prefix: `foobar <-> foobaz`
          //                            ^^^^^
          if (pattern[patternPos - 1] === word[wordPos - 1]) {
            score = 7;
          } else {
            score = 5;
          }
        } else if (
          isUpperCaseAtPos(wordPos - 1, word, wordLow) &&
          (wordPos === 1 || !isUpperCaseAtPos(wordPos - 2, word, wordLow))
        ) {
          // hitting upper-case: `foo <-> forOthers`
          //                              ^^ ^
          if (pattern[patternPos - 1] === word[wordPos - 1]) {
            score = 7;
          } else {
            score = 5;
          }
        } else if (isSeparatorAtPos(wordLow, wordPos - 2) || isWhitespaceAtPos(wordLow, wordPos - 2)) {
          // post separator: `foo <-> bar_foo`
          //                              ^^^
          score = 5;
        } else {
          score = 1;
        }
      }

      _scores[patternPos][wordPos] = score;

      const diag = _table[patternPos - 1][wordPos - 1] + (score > 1 ? 1 : score);
      const top = _table[patternPos - 1][wordPos] + -1;
      const left = _table[patternPos][wordPos - 1] + -1;

      if (left >= top) {
        // left or diag
        if (left > diag) {
          _table[patternPos][wordPos] = left;
          _arrows[patternPos][wordPos] = Arrow.Left;
        } else if (left === diag) {
          _table[patternPos][wordPos] = left;
          _arrows[patternPos][wordPos] = Arrow.Left | Arrow.Diag;
        } else {
          _table[patternPos][wordPos] = diag;
          _arrows[patternPos][wordPos] = Arrow.Diag;
        }
      } else {
        // top or diag
        if (top > diag) {
          _table[patternPos][wordPos] = top;
          _arrows[patternPos][wordPos] = Arrow.Top;
        } else if (top === diag) {
          _table[patternPos][wordPos] = top;
          _arrows[patternPos][wordPos] = Arrow.Top | Arrow.Diag;
        } else {
          _table[patternPos][wordPos] = diag;
          _arrows[patternPos][wordPos] = Arrow.Diag;
        }
      }
    }
  }

  if (_debug) {
    // eslint-disable-next-line no-console
    console.log(printTable(_table, pattern, patternLen, word, wordLen));
    // eslint-disable-next-line no-console
    console.log(printTable(_arrows, pattern, patternLen, word, wordLen));
    // eslint-disable-next-line no-console
    console.log(printTable(_scores, pattern, patternLen, word, wordLen));
  }

  _matchesCount = 0;
  _topScore = -100;
  _patternStartPos = patternStartPos;
  _firstMatchCanBeWeak = firstMatchCanBeWeak;
  _findAllMatches2(patternLen, wordLen, patternLen === wordLen ? 1 : 0, 0, false);
  if (_matchesCount === 0) {
    return undefined;
  }

  return [_topScore, _topMatch2, wordStartPos];
}

let _matchesCount = 0;
let _topMatch2 = 0;
let _topScore = 0;
let _patternStartPos = 0;
let _firstMatchCanBeWeak = false;

function _findAllMatches2(
  patternPos: number,
  wordPos: number,
  total: number,
  matches: number,
  lastMatched: boolean
): void {
  if (_matchesCount >= 10 || total < -25) {
    // stop when having already 10 results, or
    // when a potential alignment as already 5 gaps
    return;
  }

  let simpleMatchCount = 0;

  while (patternPos > _patternStartPos && wordPos > 0) {
    const score = _scores[patternPos][wordPos];
    const arrow = _arrows[patternPos][wordPos];

    if (arrow === Arrow.Left) {
      // left -> no match, skip a word character
      wordPos -= 1;
      if (lastMatched) {
        total -= 5; // new gap penalty
      } else if (matches !== 0) {
        total -= 1; // gap penalty after first match
      }
      lastMatched = false;
      simpleMatchCount = 0;
    } else if (arrow & Arrow.Diag) {
      if (arrow & Arrow.Left) {
        // left
        _findAllMatches2(
          patternPos,
          wordPos - 1,
          matches !== 0 ? total - 1 : total, // gap penalty after first match
          matches,
          lastMatched
        );
      }

      // diag
      total += score;
      patternPos -= 1;
      wordPos -= 1;
      lastMatched = true;

      // match -> set a 1 at the word pos
      matches += 2 ** wordPos;

      // count simple matches and boost a row of
      // simple matches when they yield in a
      // strong match.
      if (score === 1) {
        simpleMatchCount += 1;

        if (patternPos === _patternStartPos && !_firstMatchCanBeWeak) {
          // when the first match is a weak
          // match we discard it
          return undefined;
        }
      } else {
        // boost
        total += 1 + simpleMatchCount * (score - 1);
        simpleMatchCount = 0;
      }
    } else {
      return undefined;
    }
  }

  total -= wordPos >= 3 ? 9 : wordPos * 3; // late start penalty

  // dynamically keep track of the current top score
  // and insert the current best score at head, the rest at tail
  _matchesCount += 1;
  if (total > _topScore) {
    _topScore = total;
    _topMatch2 = matches;
  }
}

// #endregion

// #region --- graceful ---

export function fuzzyScoreGracefulAggressive(
  pattern: string,
  lowPattern: string,
  patternPos: number,
  word: string,
  lowWord: string,
  wordPos: number,
  firstMatchCanBeWeak: boolean
): FuzzyScore | undefined {
  return fuzzyScoreWithPermutations(pattern, lowPattern, patternPos, word, lowWord, wordPos, true, firstMatchCanBeWeak);
}

export function fuzzyScoreGraceful(
  pattern: string,
  lowPattern: string,
  patternPos: number,
  word: string,
  lowWord: string,
  wordPos: number,
  firstMatchCanBeWeak: boolean
): FuzzyScore | undefined {
  return fuzzyScoreWithPermutations(
    pattern,
    lowPattern,
    patternPos,
    word,
    lowWord,
    wordPos,
    false,
    firstMatchCanBeWeak
  );
}

function fuzzyScoreWithPermutations(
  pattern: string,
  lowPattern: string,
  patternPos: number,
  word: string,
  lowWord: string,
  wordPos: number,
  aggressive: boolean,
  firstMatchCanBeWeak: boolean
): FuzzyScore | undefined {
  let top = fuzzyScore(pattern, lowPattern, patternPos, word, lowWord, wordPos, firstMatchCanBeWeak);

  if (top && !aggressive) {
    // when using the original pattern yield a result we`
    // return it unless we are aggressive and try to find
    // a better alignment, e.g. `cno` -> `^co^ns^ole` or `^c^o^nsole`.
    return top;
  }

  if (pattern.length >= 3) {
    // When the pattern is long enough then try a few (max 7)
    // permutations of the pattern to find a better match. The
    // permutations only swap neighbouring characters, e.g
    // `cnoso` becomes `conso`, `cnsoo`, `cnoos`.
    const tries = Math.min(7, pattern.length - 1);
    for (let movingPatternPos = patternPos + 1; movingPatternPos < tries; movingPatternPos++) {
      const newPattern = nextTypoPermutation(pattern, movingPatternPos);
      if (newPattern) {
        const candidate = fuzzyScore(
          newPattern,
          newPattern.toLowerCase(),
          patternPos,
          word,
          lowWord,
          wordPos,
          firstMatchCanBeWeak
        );
        if (candidate) {
          candidate[0] -= 3; // permutation penalty
          if (!top || candidate[0] > top[0]) {
            top = candidate;
          }
        }
      }
    }
  }

  return top;
}

function nextTypoPermutation(pattern: string, patternPos: number): string | undefined {
  if (patternPos + 1 >= pattern.length) {
    return undefined;
  }

  const swap1 = pattern[patternPos];
  const swap2 = pattern[patternPos + 1];

  if (swap1 === swap2) {
    return undefined;
  }

  return pattern.slice(0, patternPos) + swap2 + swap1 + pattern.slice(patternPos + 2);
}

// #endregion
